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Colourful insights Calico cats, with their funky mix of orange, black and white fur, could one day help humans to lose weight.

Couch potato kitties hardly seem suited to the task, but the connection comes from their unique chromosome structure, according to research presented at the 58th Annual Biophysical Society Meeting in San Francisco.

Elizabeth Smith of the University of California, San Francisco and her colleagues explain that calico cats have an orange fur colour gene on one of their X chromosomes and a black fur colour gene on the other, so that the random silencing of one of the X's in each cell creates their distinctive patchwork coats.

"Uncovering how only one X chromosome is inactivated will help explain the whole process of epigenetic control, meaning the way changes in gene activity can be inherited without changing the DNA code," says Smith. "It can help answer other questions such as if and how traits like obesity can be passed down through generations."

The ultimate goal then is to figure out how many different kinds of genes can be turned on or off without altering the underlying DNA sequence.

A first step is to actually see specific chromosomes. Smith and her team amazingly achieved this using a new imaging technology called "soft x-ray tomography." Via fluorescence, it provides 3-D views of cellular components.

The technique enabled the researchers to look right at specific chromosomes. In this case, says Smith, they were "the inactive X chromosome of female cells."

"With new fluorescent probes, we can start identifying the position of specific genes in context — inside the tangled network of DNA within the intact nucleus," she explains.

"A cell's nucleus contains the genetic code, its DNA. But while the structure of the DNA was determined more than 50 years ago, and we're rapidly determining the position of specific genes on chromosomes, no one had visualised the DNA within an intact nucleus — an unfixed, hydrated whole cell."

Since the magnification of the instruments was extremely powerful, the researchers could see the whole substructural organisation of just a single chromosome. Each chromosome turns out to have multiple parts. It's amazing to think of all of the chromosomal complexity underlying one calico cat.

Implications for humans

Such molecules can also be responsible for X-chromosome linked disorders in humans (and there are quite a few). These can pass down family lines.

Body fat distribution has also been associated with X-chromosomes, so the possibility that regulating this thread-like structure within cell nuclei can help to control inherited tendencies toward obesity.

The research is in its infancy but scientists hope to be able to silence the obesity (and other disease-causing) components within a cell nucleus while retaining the good stuff.